The present invention relates to improvements whereby the valved control of fluid flow may be automatically linearized mechanically, and, in one particular aspect, to unique and improved servo-motor controlled valving in which a cosine-function mechanism of uncomplicated and economical construction maintains a substantially constant system resolution over its operating range.
The projected "open" area of a fluid passageway valved by way of a butterfly-type vane or ball-type plug, or the like, determines the "throughput" or amount of flow under other standard conditions, and it has of course been appreciated heretofore that relationships between angular excursions of the valve stem and the related fluid flow are non-linear for such valves. In some instances, shapings of the plugs and/or valve seats may allow the opening cross-sections to be varied approximately in linear relation to the angles to which the valve members are turned, and that linear relation thus enables an associated electrical controller to drive a servo motor and actuate the valve member with a desirable substantially-constant "transfer function" and resolution. Unless some such means is provided, the intended flow control system may be rendered unstable, and, for example, a given angular adjustment as the valve is "cracking" open will tend to have a significantly greater effect upon flow than with the same amount of angular adjustment when the valve member is nearly quarter-turned to about a fully-open position. Were the electrical controller itself required to compensate for such differences, it would have to be made to exhibit appropriately-varied gain; alternatively, some variable-gear-ratio device might attempt to approximate such variable gain mechanically.